转换为 vImage 的 CMSampleBuffer 帧颜色错误

Question

我正在尝试将 CMSampleBuffer 从相机输出转换为 vImage，然后再进行一些处理。不幸的是，即使没有任何进一步的编辑，我从缓冲区得到的帧也有错误的颜色：

实施（不考虑内存管理和错误）：

正在配置视频输出设备：

    videoDataOutput = AVCaptureVideoDataOutput()
    videoDataOutput.videoSettings = [String(kCVPixelBufferPixelFormatTypeKey): kCVPixelFormatType_32BGRA]
    videoDataOutput.alwaysDiscardsLateVideoFrames = true
    videoDataOutput.setSampleBufferDelegate(self, queue: captureQueue)
    videoConnection = videoDataOutput.connection(withMediaType:  AVMediaTypeVideo)

    captureSession.sessionPreset = AVCaptureSessionPreset1280x720

    let videoDevice = AVCaptureDevice.defaultDevice(withMediaType:  AVMediaTypeVideo)
    guard let videoDeviceInput = try? AVCaptureDeviceInput(device: videoDevice) else {
        return
    }

正在根据从相机收到的 CASampleBuffer 创建 vImage：

   // Convert `CASampleBuffer` to `CVImageBuffer`
    guard let pixelBuffer = CMSampleBufferGetImageBuffer(sampleBuffer) else { return }

    var buffer: vImage_Buffer = vImage_Buffer()
    buffer.data = CVPixelBufferGetBaseAddress(pixelBuffer)
    buffer.rowBytes = CVPixelBufferGetBytesPerRow(pixelBuffer)
    buffer.width = vImagePixelCount(CVPixelBufferGetWidth(pixelBuffer))
    buffer.height = vImagePixelCount(CVPixelBufferGetHeight(pixelBuffer))

    let vformat = vImageCVImageFormat_CreateWithCVPixelBuffer(pixelBuffer)
    let bitmapInfo:CGBitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.last.rawValue | CGBitmapInfo.byteOrder32Little.rawValue)

    var cgFormat = vImage_CGImageFormat(bitsPerComponent: 8,
                                        bitsPerPixel: 32,
                                        colorSpace: nil,
                                        bitmapInfo: bitmapInfo,
                                        version: 0,
                                        decode: nil,
                                        renderingIntent: .defaultIntent)

     // Create vImage
     vImageBuffer_InitWithCVPixelBuffer(&buffer, &cgFormat, pixelBuffer, vformat!.takeRetainedValue(), cgColor, vImage_Flags(kvImageNoFlags))

正在将缓冲区转换为 UIImage：

为了测试，CVPixelBuffer 导出到 UIImage，但将其添加到视频缓冲区具有相同的结果。

var dstPixelBuffer: CVPixelBuffer?

    let status = CVPixelBufferCreateWithBytes(nil, Int(buffer.width), Int(buffer.height),
                                              kCVPixelFormatType_32BGRA, buffer.data,
                                              Int(buffer.rowBytes), releaseCallback,
                                              nil, nil, &dstPixelBuffer)

    let destCGImage = vImageCreateCGImageFromBuffer(&buffer, &cgFormat, nil, nil, numericCast(kvImageNoFlags), nil)?.takeRetainedValue()

    // create a UIImage
    let exportedImage = destCGImage.flatMap { UIImage(cgImage: [=12=], scale: 0.0, orientation: UIImageOrientation.right) }

    DispatchQueue.main.async {
        self.previewView.image = exportedImage
    }

Answer 1

对 vImageBuffer_InitWithCVPixelBuffer 的调用正在执行修改您的 vImage_Buffer 和 CVPixelBuffer 的内容，这有点调皮，因为在您的（链接的）代码中您保证不会修改当你说

时的像素

CVPixelBufferLockBaseAddress(pixelBuffer, .readOnly)

为 BGRA8888 初始化 CGBitmapInfo 的正确方法是 alpha 优先，32 位小尾数法，这是不明显的，但包含在 vImage_Utilities.h 中 vImage_CGImageFormat 的头文件中：

let bitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.first.rawValue | CGImageByteOrderInfo.order32Little.rawValue)

我不明白为什么 vImageBuffer_InitWithCVPixelBuffer 正在修改您的缓冲区，因为 cgFormat (desiredFormat) 应该匹配 vformat，尽管它被记录为修改缓冲区，所以也许你应该先复制数据。

Answer 2

尝试为您的 CV 图片格式设置颜色 space：

    let vformat = vImageCVImageFormat_CreateWithCVPixelBuffer(pixelBuffer).takeRetainedValue()

    vImageCVImageFormat_SetColorSpace(vformat,
                                      CGColorSpaceCreateDeviceRGB())

...并更新您对 vImageBuffer_InitWithCVPixelBuffer 的调用以反映 vformat 现在是托管引用这一事实：

    let error = vImageBuffer_InitWithCVPixelBuffer(&buffer, &cgFormat, pixelBuffer, vformat, nil, vImage_Flags(kvImageNoFlags))

最后，您可以删除以下行，vImageBuffer_InitWithCVPixelBuffer 正在为您完成这项工作：

//        buffer.data = CVPixelBufferGetBaseAddress(pixelBuffer)
//        buffer.rowBytes = CVPixelBufferGetBytesPerRow(pixelBuffer)
//        buffer.width = vImagePixelCount(CVPixelBufferGetWidth(pixelBuffer))
//        buffer.height = vImagePixelCount(CVPixelBufferGetHeight(pixelBuffer))

请注意，您不需要锁定 Core Video 像素缓冲区，如果您查看 headerdoc，它会显示 "It is not necessary to lock the CVPixelBuffer before calling this function"。

转换为 vImage 的 CMSampleBuffer 帧颜色错误

CMSampleBuffer frame converted to vImage has wrong colors

swift

avfoundation

accelerate-framework

cvpixelbuffer

vimage